1. Field of the Invention
The present invention relates to a semiconductor device and a photonic semiconductor device applying the semiconductor device.
2. Description of the Background Art
A major failure of laser diodes is known as an optically caused facet breakdown (COD; catastrophic optical damage). One conventional measure to counter the COD of a laser diode involves including facets with a window structure that will not absorb any laser beam, thus boosting the laser diode in reliability.
The window structure constitutes light-non-absorbing regions interposed between an active layer inside the laser diode and the facets of the laser diode. The light-non-absorbing regions have a wider band gap energy than the active layer in order to eliminate laser beam absorption. The light-non-absorbing regions, along with the active layer, are covered with a cladding layer. The cladding layer, in turn, is topped with a contact layer opposite the active layer and with current-unfed regions opposite the light-non-absorbing regions and contiguous with the contact layer.
The contact layer and current-unfed regions are covered with a metal electrode layer. A plating layer is formed on the metal electrode layer. The plating layer and metal electrode layer introduce carriers into the active layer through the contact layer and cladding layer, triggering laser light emission by the active layer based on its band gap and quantum level. The current-unfed regions are used to forestall current flows from the metal electrode layer into the cladding layer and light-non-absorbing regions underneath. The plating layer serves to facilitate die bonding and wire bonding of the photonic semiconductor device as well as to stabilize and reinforce the bonding of the device.
When laser diodes are cut from a wafer, it is customary to cleave the wafer into the diodes so that each diode will have facets with a mirror surface. In such cases, the plating layer is spaced from the cleaving positions because the plating layer hampers cleavage. On the other hand, the light-non-absorbing regions are contiguous with the laser diode facets to prevent optical damage to the facets. In this structure, the current blocking regions opposite the light-non-absorbing regions are also contiguous with the laser diode facets. As a result, the plating layer is farther inside the laser diode than a boundary between the contact layer and the current-unfed regions on the metal electrode layer. In other words, the plating layer is not located opposite the current-unfed regions.
In the plating layer arrangement outlined above, a disproportionately elevated local density of currents has been observed in the metal electrode layer between a plating layer end and the current-unfed regions. The heightened local current density leads to local heating and device breakdown.
The present invention has been conceived to solve the previously-mentioned problems and a general object of the present invention is to provide a novel and useful semiconductor device, and is to provide a novel and useful photonic semiconductor device.
A more specific object of the present invention is to prevent localized increases in current density, and is to relieve local heating.
The above object of the present invention is attained by a following semiconductor device and a following photonic semiconductor device.
According to one aspect of the present invention, the semiconductor device comprises: a contact layer; current-unfed regions contiguous with the contact layer; a metal electrode layer coupled both to the contact layer and to each of the current-unfed regions and having a thickness of xe2x80x9cwxe2x80x9d; and a plating layer which is formed on the metal electrode layer, which has a thickness of xe2x80x9cDxe2x80x9d, and which has facets each located a predetermined distance away from a boundary between the contact layer and each of the current-unfed regions; wherein, if it is assumed that the boundary between the contact layer and any one of the current-unfed regions is taken as an origin, that a direction from the origin toward the any one of the current-unfed regions is a negative direction, and that a direction from the origin toward the contact layer is a positive direction, then the distance xe2x80x9cdxe2x80x9d between the origin and each of the facets of the plating layer satisfies a relationship of d/w*[1xe2x88x92w/(w+D)] less than 20.
According to another aspect of the present invention, the photonic semiconductor device comprises: an active layer; light-unabsorbing regions contiguous with the active layer; a clad layer covering the active layer and the light-unabsorbing regions; a contact layer located above the clad layer which is on the active layer; current-unfed regions contiguous with the contact layer and over the light-unabsorbing regions; a metal electrode layer covering the contact layer and the current-unfed regions and having a thickness of xe2x80x9cwxe2x80x9d; and a plating layer which is formed on the metal electrode layer, which has a thickness of xe2x80x9cDxe2x80x9d, and which has facets each located a predetermined distance away from a boundary between the contact layer and each of the current-unfed regions; wherein, if it is assumed that the boundary between the contact layer and any one of the current-unfed regions is taken as an origin, that a direction from the origin toward the any one of the current-unfed regions is a negative direction, and that a direction from the origin toward the contact layer is a positive direction, then the distance xe2x80x9cdxe2x80x9d between the origin and each of the facets of the plating layer satisfies a relationship of d/w*[1xe2x88x92w/(w+D)] less than 20.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.